CS162 - Topic #2

1. CS162 - Topic #2 • New Topic: • Programming paradigms in C++ • Data Abstraction and Abstract Data Types • Programming Assignment Questions • Begin on Stage #1

2. CS162 - Programming Paradigms • The most important aspect of C++ is its ability to support many different programming paradigms • We will cover this term • procedural abstraction • modular abstraction • data abstraction • as ways or techniques used to solve problems

3. CS162 - Procedural Abstraction • This is where you build a “fence” around program segments, preventing some parts of the program from “seeing” how tasks are being accomplished. • Any use of globals causes side effects that may not be predictable, reducing the viability of procedural abstraction

4. CS162 - Procedural Abstraction • This may be the approach taken with stage #1...where the major tasks are broken into functions. • You can test your functions separately before the entire program is written and debugged.

5. CS162 - Modular Abstraction • With modular abstraction, we build a “screen” surrounding the internal structure of our program prohibiting programmers from accessing the data except through specified functions. • Many times data structures (e.g., structures) common to a module are placed in a header files along with prototypes (allows external references)

6. CS162 - Modular Abstraction • The corresponding functions that manipulate the data are then placed in an implementation file. • Modules (files) can be compiled separately, allowing users access only to the object (.o) files • We progress one small step toward OOP by thinking about the actions that need to take place on data...

7. CS162 - Modular Abstraction • Later this term we will be implementing modular abstraction by separating out various functions/structures/classes into multiple .cpp and .h files. • .cpp files contain the implementation of our functions • .h files contain the prototypes, class and structure definitions.

8. CS162 - Modular Abstraction • We then include the .h files in modules that need access to the prototypes, structures, or class declarations: • #include “myfile.h” • (Notice the double quotes!) • We then compile the programs by: • g++ main.cpp myfile.cpp • (Notice no .h file is listed on the above line)

9. CS162 - Data Abstraction • Data Abstraction is one of the most powerful programming paradigms • It allows us to create our own user defined data types (using the class construct) and • then define variables (i.e., objects) of those new data types.

10. CS162 - Data Abstraction • With data abstraction we think about what operations can be performed on a particular type of data and not how it does it • Here we are one step closer to object oriented programming

11. CS162 - Data Abstraction • Data abstraction is used as a tool to increase the modularity of a program • It is used to build walls between a program and its data structures • what is a data structure? • talk about some examples of data structures • We use it to build new abstract data types

12. CS162 - Data Abstraction • An abstract data type (ADT) is a data type that we create • consists of data and operations that can be performed on that data • Think about an char type • it consists of 1 byte of memory and operations such as assignment, input, output, arithmetic operations can be performed on the data

13. CS162 - Data Abstraction • An abstract data type is any type you want to add to the language over and above the fundamental types • For example, you might want to add a new type called: list • which maintains a list of data • the data structure might be an array of structures • operations might be to add to, remove, display all, display some items in the list

14. CS162 - Data Abstraction • Once defined, we can create lists without worrying about how the data is stored • We “hide” the data structure used for the data within the data type -- so it is transparent to the program using the data type • We call the program using this new data type: the client program (or client)

15. CS162 - Data Abstraction • Once we have defined what data and operations make sense for a new data type, we can define them using the class construct in C++ • Once you have defined a class, you can create as many instances of that class as you want • Each “instance” of the class is considered to be an “object” (variable)

16. CS162 - Data Abstraction • Think of a class as similar to a data type • and an object as a variable • And, just as we can have zero or more variables of any data type... • we can have zero or more objects of a class! • Then, we can perform operations on an object in the same way that we can access members of a struct...

17. CS162 - Example • For a list of videos, we might start with a struct defining what a video is: struct video { char title[100]; char category[5]; int quantity; };

18. CS162 - Example • For a list of videos data type: class list { public: list(); int add (const video &); int remove (char title[]); int display_all(); private: video my_list[CONST_SIZE]; int num_of_videos; };

19. CS162 - Example • For a client to create a list object: main() { list home_videos; //has an array of 100 videos list kids_shows; //another 100 videos here... ••• video out_of_site; cin.get(out_of_site.title,100,’\n’); cin.ignore(100,’\n’); ••• home_videos.add(out_of_site); //use operation

20. CS162 - For Next Time • Study classes...we’ll look at terminology • Next time we will discuss: • class constructors • where to place the class “interface” we saw previously and • where to place the implementation of the “member functions”